Multiple Choice Question (MCQ) of Alternator and Synchronous Motors page-8

71. For given output, steam turbo-alternators are smaller in size than water turbine alternators for the following reason

a) steam turbo-alternators have long speeds
b) steam turbo-alternators run at higher speed
c) steam turbo-alternators are built with smaller capacities
d) none of these

Ans: (b)

72. In a large alternator, the moving part is

a) the poles
b) armature
c) brushes
d) none of these

Ans: (a)

73. To reverse the phase sequence of voltage generated in an alternator, we should

a) reverse the connection of its field winding
b) interchange any two of its phase terminals
c) both (a) and (b)
d) none of these

Ans: (c)

74. The length 1 of the rotor of a turbo-alternator and its diameter D are related as below

a) ɭ = D/2
b) ɭ = D
c) ɭ = 2D
d) ɭ >> D

Ans: (d)

75. If the terminal voltage of an alternator is required to decrease with increases of load, the pf of the load should be

a) zero lagging
b) zero leading
c) unity
d) more than unity

Ans: (b)

76. Short pitch coils are used in alternators

a) to reduce the size of the machine
b) to reduce the stray losses
c) to reduce harmonic output
d) to reduce accurate phase shift of 120° between each phase

Ans: (c)

77. The most accurate method of measuring the hot spot temperature in field winding is

a) thermocouple method
b) thermometer method
c) by measuring the increase in winding resistances
d) none of these

Ans: (a)

78. Distributing the armature winding of alternator in more than one number of slop per pole per phase results in

a) economy of material used in winding
b) reduction of irregularities produced in waveform
c) less weight of the entire armature
d) increase of generated emf per phase

Ans: (b)

79. Regulation of an alternator is likely to be negative case of

a) high speed alternators
b) low speed alternators
c) lagging power factor of the load
d) leading power factor of the load

Ans: (d)

80. Maximum power in a synchronous machine is obtained when the load angle is

a) 0°
b) 85°
c) 120°
d) 135°

Ans: (b)

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Multiple Choice Question (MCQ) of Alternator and Synchronous Motors page-8

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